In a present Wireless Local Area Networks (WLAN), an Access Point (AP) and a plurality of stations (STA) associated with the AP may constitute a Basic Service Set (BSS). A central AP and stations in a network may use a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanism to share channels. In this mechanism, there is an issue of collision due to hidden stations. For example, as shown in FIG. 1, station A is located in coverage of BSS 1, station B is located in coverage of BSS 2, and station D is located in coverage of BSS 3. Since the coverage of BSS 1 and BSS 2 does not overlap with each other, station A and station B cannot sense each other. However, station A and station B both can communicate with another station C. Therefore, when station A and station B both communicate with station C simultaneously, collision will occurs based on the CSMA/CA mechanism.
In order to solve the issue of collision due to hidden stations, the Institute of Electrical and Electronic Engineers (IEEE) presents a virtual channel detection mechanism. In this mechanism, by including subscription channel duration information in header of a radio frame, an overhearing station that receives a radio frame including the subscription channel duration information may set a locally stored network allocation vector (NAV), value of which may be set to the maximum value of the subscription channel duration information. During this duration, the overhearing station does not transmit data, thus avoiding contention channel by the hidden stations. After the NAV being reduced to zero, the overhearing station can content channel for transmitting data. As shown in FIG. 2, a schematic diagram of delay access to a channel by an overhearing station according to settings of NAV is illustrated. In FIG. 2, RTS refers to a Request To Send frame, and CTS refers to a Clear To Send frame.
However, in some situations, the overhearing station does not acquire the duration information. Then, the overhearing station must wait for at least an Extended Interframe Space (EIFS) after receiving a radio frame to access channel when a receiving station returns an acknowledgment (ACK) by default in the EIFS. In practice, the receiving station may return an ACK, a BlockACK, data, or no response. In this case, EIFS is not accurate enough. With respect to this case, IEEE defines early ACK indication in which 2 bits in signaling field of physical frame header are used as ACK indication. Different settings of ACK indication are used to indicate the following 4 cases:                1) no response;        2) ACK;        3) BlockACK;        4) non-ACK, non-BlockACK or non-CTS frame.        
Correspondingly, IEEE presents a channel virtual carrier detection mechanism, i.e., Response Indication Deferral (RID). In this mechanism, an RID timer is defined according to the ACK indication field in which different duration of the RID timer is defined according to different settings of the ACK indication. In addition, the value of the RID timer may be reset upon receiving a new PHY-RXSTART.indication.
The settings of RID timer are different with that of NAV in that: the value of NAV is updated with the greater value of the newly acquired duration value and the current value of NAV; the value of the RID timer is updated by replacing the old value with a new value, as shown in FIG. 3. FIG. 3 is a schematic diagram of delay access to a channel by an overhearing station according to settings of RID timer. Additionally, the value of RID timer will be reset as long as appearance of a new RXSTART. Since the value of RID timer is obtained through a rough estimate, the accuracy thereof is less than NAV settings. However, the setting of value of RID timer is simply implemented by parsing the physical frame header which is advantageous for energy-saving.
In the related art, when a station receives a radio frame containing ACK indication and duration both, the station may update the value of NAV according to the value of duration in the radio frame, and set the value of RID timer according to the ACK indication contained in the radio frame. In accordance with the meaning of virtual carrier detection, as long as one of the NAV and the RID timer is not 0, then it is considered that the channel is busy. When the roughly estimated value of RID timer is greater than the accurately estimated value of NAV, the overhearing station will access to channel according to the value of RID timer rather than the accurate value of channel subscription duration NAV, which is not advantageous for fast accessing to channel by the overhearing station. As shown in FIG. 4, a schematic diagram of delay access to a channel by an overhearing station according to settings of NAV and RID timer is illustrated.